A monthly water balance model for evaluation of climate change impacts on the streamflow of Ginganga and Kelani ganga basins, Sri lanka

The availability and distribution of freshwater resources will be greatly affected by climate change and the vulnerability to water scarcity of affected populations currently experience could increase. Studies relating climate change and hydrology are becoming prevalent but few published studies focus on changes in Sri Lanka streamflow. There is ample evidence to suggest that the climate of South Asian region has already changed. Climate change or its increased variability is expected to alter the timing and magnitude of runoff. As a result it has important implications for existing water resources systems as well as for future water resources planning and management. A two-parameter monthly water balance model is adopted to simulate the runoff for the evaluation of climate change impacts on the streamflow of two major catchments in Kelani Ganga and Gin Ganga basins in Sri Lanka. The model was successfully calibrated and verified for Kelani Ganga & Gin Ganga basins showing that average values of 0.485 and 1110.50 mm for parameters c & SC respectively could simulate monthly streamflow with average MRAE 0.088 and average Nash-Sutcliffe efficiency 0.957. Application results show that the model efficiencies are high in both the calibration and verification periods. This study demonstrated the models capability and applicability to evaluate the climate change impacts on the streamflow and also to forecast for future scenarios. It is suggested that this two parameter model can be easily and efficiently incorporated in the climate impact studies to simulate monthly runoff and as well as in the water resources planning program